BACKGROUND Primary malignant melanoma of the vagina is extremely rare, accounting for 0.3-0.8% of all malignant melanomas. True amelanotic vaginal melanoma showing no melanin on histological examination is exceedingly rare, accounting for only 2% of all vaginal melanomas. METHODS We describe a 31-year-old female patient who presented with locally advanced amelanotic melanoma of the vagina, with no evidence of metastatic spread on the computerized tomography (CT) scan, but who was subsequently diagnosed as suffering from metastatic disease by positron emission tomography (PET)-CT performed a few weeks following posterior pelvic exenteration. CONCLUSIONS Specific immunohistochemical staining with melanoma markers should be performed to confirm or exclude a diagnosis of amelanotic melanoma in all patients presenting with a vaginal mass composed of undifferentiated epithelioid malignant cells. Fluorodeoxyglucose (FDG)-PET-CT should be performed as part of the preoperative evaluation, to identify the presence or absence of metastatic disease in all patients with vaginal melanoma.